Suggest instance variable names in case "@" is missing

closes #12, but class/module variable name suggestion should also be
implemented.

lib/did_you_mean/finders/name_error_finders/similar_name_finder.rb

@@ -1,16 +1,19 @@
 module DidYouMean
   class SimilarNameFinder
     include BaseFinder
-    attr_reader :name, :_methods, :_local_variables
+    attr_reader :name, :_methods, :_local_variables, :_instance_variables
 
     def initialize(exception)
       @name             = exception.name
       @_methods         = exception.frame_binding.eval("methods")
       @_local_variables = exception.frame_binding.eval("local_variables")
+      @_instance_variables = exception.frame_binding.eval("instance_variables").map do |name|
+        name.to_s.tr("@", "")
+      end
     end
 
     def words
-      local_variable_names + method_names
+      local_variable_names + method_names + instance_variable_names
     end
 
     alias target_word name
@@ -31,6 +34,14 @@ def similar_methods
       similar_words.select{|word| word.is_a?(MethodName) }
     end
 
+    def instance_variable_names
+      _instance_variables.map {|word| InstanceVariableName.new(word.to_s) }
+    end
+
+    def similar_instance_variables
+      similar_words.select {|word| word.is_a?(InstanceVariableName) }
+    end
+
     def format(word)
       "#{word.prefix}#{word}"
     end
@@ -42,5 +53,9 @@ def prefix; "#"; end
     class LocalVariableName < String
       def prefix; ""; end
     end
+
+    class InstanceVariableName < String
+      def prefix; "@"; end
+    end
   end
 end

test/similar_name_finder_test.rb

@@ -2,9 +2,16 @@
 
 class SimilarNameFinderTest < Minitest::Test
   class User
+    def initialize(options = {})
+      @email = options[:email]
+    end
+
     def call_flrst_name;  f1rst_name; end
     def call_fr0m_module; fr0m_module; end
     def first_name; end
+    def to_s
+      "#{@first_name} #{@last_name} <#{email}>"
+    end
   end
 
   module UserModule
@@ -16,6 +23,7 @@ def setup
 
     @error_from_instance_method = assert_raises(NameError){ user.call_flrst_name }
     @error_from_module_method   = assert_raises(NameError){ user.call_fr0m_module }
+    @error_from_missing_at_sign = assert_raises(NameError){ user.to_s }
 
     # Use begin + rescue as #assert_raises changes a scope.
     @error_from_local_variable  = begin
@@ -29,6 +37,7 @@ def test_similar_words
     assert_includes @error_from_instance_method.finder.similar_words, "first_name"
     assert_includes @error_from_module_method.finder.similar_words,   "from_module"
     assert_includes @error_from_local_variable.finder.similar_words,  "user"
+    assert_includes @error_from_missing_at_sign.finder.similar_words, "email"
   end
 
   def test_similar_instance_methods
@@ -40,9 +49,14 @@ def test_similar_local_variables
     assert_includes @error_from_local_variable.finder.similar_local_variables, "user"
   end
 
+  def test_similar_instance_variables
+    assert_includes @error_from_missing_at_sign.finder.similar_instance_variables, "email"
+  end
+
   def test_did_you_mean?
     assert_match "Did you mean? #first_name",  @error_from_instance_method.did_you_mean?
     assert_match "Did you mean? #from_module", @error_from_module_method.did_you_mean?
     assert_match "Did you mean? user",         @error_from_local_variable.did_you_mean?
+    assert_match "Did you mean? @email",       @error_from_missing_at_sign.did_you_mean?
   end
 end